On 13-2-2008 22:06 Tobias Brox wrote:
> What I'm told is that the state-of-the-art SAN allows for
> an "insane amount" of hard disks to be installed, much more than what
> would fit into any decent database server. We've ended up buying a SAN,
> the physical installation was done last week, and I will be able to tell
> in some months if it was a good idea after all, or not.
Your SAN-pusher should have a look at the HP-submissions for TPC-C...
The recent Xeon systems are all without SAN's and still able to connect
hundreds of SAS-disks.
This one has 2+28+600 hard drives connected to it:
http://tpc.org/results/individual_results/HP/hp_ml370g5_2p_X5460_tpcc_080107_es.pdf
Long story short, using SAS you can theoretically connect up to 64k
disks to a single system. And with the HP-example they connected 26
external enclosures (MSA70) to 8 internal with external SAS-ports. I.e.
they ended up with 28+600 harddrives spread out over 16 external 4-port
SAS-connectors with a bandwidth of 12Gbit per connector...
Obviously its a bit difficult to share those 628 harddrives amongst
several systems, but the argument your colleagues have for SAN isn't a
very good one. All major hardware vendors nowadays have external
SAS-enclosures which can hold 12-25 external harddrives (and can often
be stacked to two or three enclosures) and can be connected to normal
internal PCI-e SAS-raid-cards. Those controllers have commonly two
external ports and can be used with other controllers in the system to
combine all those connected enclosures to one or more virtual images, or
you could have your software LVM/raid on top of those controllers.
Anyway, the common physical limit of 6-16 disks in a single
server-enclosure isn't very relevant anymore in an argument against SAN.
Best regards,
Arjen